| Electronics > Beginners |
| Transistor Cross Reference help - Yamaha DX7S switching power supply |
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| grantb5:
R2 and R3 both open, I'll have to recheck R9 since you've asked. No visible signs of failure though. Q1 and Q2 both toast. I just did a Yamaha SPX90 power supply fix (I got suckered twice by the "but it's so cheap! I have to buy it!" bug) and that one is somewhat similar, but the failure was all electrolytics that spilled their guts and the glue on the PCB, it ate one film cap and one resistor. I just had to replace passives in that one and built up the confidence for this task. Kind of. |
| floobydust:
I would consider FJPF13007 H2 $1.39 as a replacement. NTE parts can be confusing because they will use a 500V transistor to cover all the 300-400V parts as well. Note the hFE is lower for NTE2337 compared to 2SC3570. Non-isolated TO-220 parts will generate more EMI as the heatsink will have high-voltage switching pulses present, and you need to ensure HV spacings to nearby parts is enough. I would stay with the fullpack, and use fusible resistors where they are spec'd. |
| grantb5:
Thanks. I never really gave a second thought to "fullpack". I knew the original TO-220 was "isolated" (insulated) but didn't connect the fullpack dots. (It didn't help that I was sourcing a PCB from Japan hours earlier and the guy there referred to it as "loose pack" which I guess is his translation for PCB-only.) But interesting to know about the EMI. The pads for the heatsink are unconnected so any regular TO-220 I would have just screwed right in there without a second thought. I will check out that part for sure. :palm: The service manual calls R2 and R3 metal oxide film and those are obtainable. As far as I know only those two resistors, plus Q1 and Q2 are fried. I'll probably recap the electrolytics, which isn't my thing, but after my SPX90 fix, I think it's warranted for <$20. All of them measure OK on a simple meter. I don't think this thing died a natural death. The power switch was missing and a small toggle switch was duct-taped in instead. Plus another PCB was crushed. Those have been replaced/restored. |
| vk6zgo:
--- Quote from: grantb5 on February 11, 2019, 11:16:57 pm ---Thanks. I never really gave a second thought to "fullpack". I knew the original TO-220 was "isolated" (insulated) but didn't connect the fullpack dots. (It didn't help that I was sourcing a PCB from Japan hours earlier and the guy there referred to it as "loose pack" which I guess is his translation for PCB-only.) But interesting to know about the EMI. The pads for the heatsink are unconnected so any regular TO-220 I would have just screwed right in there without a second thought. I will check out that part for sure. :palm: The service manual calls R2 and R3 metal oxide film and those are obtainable. As far as I know only those two resistors, plus Q1 and Q2 are fried. I'll probably recap the electrolytics, which isn't my thing, but after my SPX90 fix, I think it's warranted for <$20. All of them measure OK on a simple meter. I don't think this thing died a natural death. The power switch was missing and a small toggle switch was duct-taped in instead. Plus another PCB was crushed. Those have been replaced/restored. --- End quote --- The switching transistors in most BJT SMPS are fairly generic. I routinely replaced the "2S" series devices in the PSU of Sony KX27 "Profeel"picture monitors with BU208D devices. It helped that I could use them to replace the horizontal output transistors as well. If the switching transistor has failed, I would be quite suspicious of transformer T1. In one of the Profeels, the transistor initially failed short circuit, but as the thing was slung up above head height, & had no input, nobody noticed. It sat there for weeks till somebody tried to use it, giving the output of the rectifier bridge plenty of time to "cook" the transformer. It "looked" OK, but had shorted turns. After rebuilding the supply, it went "bang" upon initial turn on! :-[ |
| grantb5:
Thanks for the tip. Not sure I can asses that part and certainly cannot find the original. If it dies again I may try and wedge some other power supply in. |
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